1. Field of the Invention
The present invention relates to a spin-current switched magnetic memory element having a plurality of layers (e.g., magnetic layers) and a method of fabricating the memory element, and more particularly, to a spin-current switched magnetic memory element including a plurality of layers, in which at least one of the magnetic layers has a perpendicular magnetic anisotropy component. The memory element has the switching threshold current and device impedance suitable for integration with complementary metal oxide semiconductor (CMOS) integrated circuits.
2. Description of the Related Art
Spin-current injection switches represent a new class of memory devices that can be scaled down to the size of at least about 10 nm. These devices use spin polarized current injection to switch magnetic bits.
There is an intense search for a two terminal current-switchable spin-valve or magnetic tunneling-based device for memory applications. If such devices can be found with adequate switching current for writing and proper impedance and signal level for reading, it will bring possibilities for a new architecture to magnetic random access memory (MRAM).
For a thin film nanomagnet memory element, the threshold current necessary to induce such a switch is directly proportional to the combined magnetic anisotropy (4πMs+H), where 4πMs is the easy-plane shape anisotropy, and H represents the additional uniaxial anisotropy and/or applied magnetic field.
However, the experimentally demonstrated threshold current for a thin film nanomagnet of 60 nm×120 nm×2 nm is about 1 mA. This required current is too high (e.g., by at least an order of magnitude) for successful insertion of these devices into current-generation complementary metal oxide semiconductor (CMOS) circuits.
In addition, to date all spin transfer-switching devices use the metal-based current perpendicular (CPP) spin valve structure, which has too low an impedance for fast read-out using a CMOS-based circuit. Magnetic tunneling junctions will have higher impedances that can be compatible with CMOS requirements. However, to date no clear demonstration has been made that such spin-transfer-based magnetic switching exists in magnetic tunneling junctions. This is because of two factors.
First, the normal, magnetization-in-plane magnetic film has too large an easy-plane de-magnetization field (e.g., on the order of 1.8 Tesla for cobalt, for example), which causes the switching current density to be too high (e.g., on the order of 107 A/c m2), as measured using a spin-valve type of switches, which has been demonstrated by the inventors as well as others. Secondly, the breakdown current density is too low in magnetic tunneling devices, typically below 105 A/cm2, for successful combination of a tunneling device with a spin-transfer switch.
Thus, two terminal current-switchable spin-valve or magnetic tunneling-based devices have not been efficiently and effectively used for conventional magnetic memory applications.